Method for producing a dentist tool

ABSTRACT

Method for producing a dentist tool formed by an overlay to be used by a dentist in removing tooth structure, said method comprising the steps of: acquiring three-dimensional data relating to a shape of a tooth and at least a part of a neighbouring tooth; processing said three-dimensional data with a computer so as to determine an overlay fitting said tooth and fitting at least said part of said neighbouring tooth; further processing said three-dimensional data with said computer so as to determine a predetermined part of tooth structure to be removed from said tooth so as to prepare said tooth for further treatment; determining at least two guiding edges of which a first and a second guiding edge are spaced apart from each other by a distance d of at least 0.5 mm, said guiding edges being configured so as to enable said dentist cutting tool to be guided by simultaneously contacting said first and said second guiding edge in such a manner as to enable a guided removal of at least partially said predetermined part of tooth structure; producing said determined overlay having said determined guiding edges.

The present application is a continuation of U.S. patent applicationSer. No. 14/170,120 filed Jan. 31, 2014, which is a continuation of U.S.patent application Ser. No. 12/698,777 filed Feb. 2, 2010, now U.S. Pat.No. 8,640,338, and is a continuation-in-part of U.S. patent applicationSer. No. 12/364,216 filed Feb. 2, 2009, now abandoned, the disclosuresof which are hereby incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention concerns a method for producing a dentist toolformed by an overlay to be used by a dentist in removing tooth structurefrom a tooth, said method comprising the steps of:

determining a predetermined part of tooth structure to be removed so asto prepare said tooth for further treatment;

determining an overlay fitting said tooth and fitting at least a part ofa neighboring tooth of said tooth;

simulating a movement to be followed by a dentist cutting tool in orderto remove at least a part of said predetermined part;

determining a first guiding edge within said overlay, said first guidingedge corresponding to said movement so that it is provided to contactsaid dentist cutting tool following said movement, thereby beingprovided to guide said dentist cutting tool in a predetermined position,said first guiding edge being part of a guiding means;

producing said determined overlay with said guiding means.

The present invention further concerns a dentist tool to be used by adentist in removing tooth structure from a tooth of a patient, whichtooth is to be prepared for further treatment, said dentist toolcomprising:

an overlay having a shape and dimensions so that it is releasablyfixable over said tooth and being attachable to that tooth or to atleast a part of a neighboring tooth of said tooth;

a first guiding edge within said overlay that is provided to contact adentist cutting tool following a predetermined movement, said firstguiding edge thereby being provided to guide said dentist cutting in apredetermined position.

When a patient needs a crown, bridge, onlay, inlay, veneer, or otherrestoring or other dental prosthesis and/or aesthetic tooth treatment,conventionally, during an initial office visit, the dentist identifiesthe needs of the patient and determines an appropriate treatment. Duringsubsequent visits, in case the tooth comprises damaged and/or infectedtooth structure, the dentist removes this tooth structure andreconstructs the tooth as much as possible using conventionaltechniques. Thereafter, the dentist performs the final preparation ofthe tooth for further treatment by removing tooth material, which is tobe interpreted as original tooth structure and reconstructed toothstructure, with a dental cutting tool such as a high-speed drill.Relying upon eyesight and expertise, the dentist uses the drill to shapethe tooth in a form that is suitable for further treatment, inparticular a form onto which a crown, bridge, onlay, inlay, veneer orother tooth restoring part can be mounted. Then, the dentist takes animpression of the dental arch in which the prepared tooth is located,and sends the impression to the dental laboratory to have the dentaltechnician make the restoration part. Using the impression of theprepared tooth, the dental technician produces a restoration part thatmatches the color, geometrical and material specifications, and sends itto the dentist. At the patient's final visit, the dentist adjusts therestoration part as necessary before fitting it in place.

A further dentist tool is disclosed in EP1547544. This dentist tooldecreases the impact of the experience and expertise of the dentist ontothe treatment, and it is used by a dentist in boring an artificial toothroot cavity. In EP1547544, guiding means, formed by a cylindrical hole,for guiding a drill in a straight-forward way, is provided. In such amanner an artificial tooth root cavity can be bored with greaterprecision even by a less experienced dentist. Moreover a suitable rootcavity position can be calculated based on the information processed bythe computer, so as to form in the most optimal way a cavity in the jawbone.

A drawback of the known dentist tool is that it can only be used by adentist in boring holes into the jaw bone. This dentist tool is notsuitable to be used by a dentist in preparing a tooth for furthertreatment.

A further dentist tool is disclosed in DE4012327, which is consideredclose prior art. This dentist tool is formed by a template thatcomprises a guiding edge for guiding a dentist cutting tool along apredetermined movement. The guiding edge is provided at a predeterminedheight so that besides the position, also the depth of the dentistcutting tool can be guided. DE4012327 furthermore teaches how thedentist can use the template by placing the template in the mouth of theperson and, using a moving-plate fixing the tilt of the dentist cuttingtool into a predetermined inclination, running with the dentist cuttingtool along the guiding edge thereby removing predetermined toothstructure.

A drawback of this known dentist tool is that the tilt is, because ofthe moving-plate, fixed in a predetermined inclination. Thereby, thedentist tool cannot guide a dentist cutting tool in a complex movementwhere also tilt variations occur. In particular when working withcomplex surfaces such as teeth, such complex movements are preferable.

It is an object of the present invention to provide method for producinga dentist tool that is suitable for guiding a dentist cutting tool alonga complex movement.

To this end, the method for producing a dentist tool according to thepresent invention is characterized in that said method comprises thefurther steps of:

determining a second guiding edge within said overlay that is spacedapart from said first guiding edge by a distance d of at least 0.5 mm,said second guiding edge corresponding to said movement so that it isprovided to simultaneously with said first guiding edge contact saiddentist cutting tool following said movement, said first and secondguiding edge thereby being provided to guide said dentist cutting toolin a predetermined tilt, said second guiding edge being part of saidguiding means.

The presence of the second guiding edge in the overlay results thereinthat the movement of a dentist cutting tool can be guided along apredetermined surface, whereas, in the prior art, the movement of thetool can only be guided along a predetermined line. Thereby also aguidance of the inclination of the dentist cutting tool can be obtained,which is not possible in the prior art. The presence of the secondguiding edge results in that a dentist cutting tool can be guided alongcomplex movements where position variations as well as tilt variationsoccur.

The determination of a predetermined part of tooth structure to beremoved has the effect that this does not any more depend on the skillsof the dentist. Determining and producing guiding edges into an overlay,which guiding edges are suitable for simultaneously contacting thedentist cutting tool, allows the cutting tool to be guided along a welldetermined path in an at least partially predetermined way. The overlay,having the guiding edges, accurately indicates onto the tooth the partto be removed from the tooth as determined by the computer. Moreover thetool according to the invention is provided to assist the dentist inremoving tooth structure as the tool allows a dentist to remove at leastpart of a predetermined part of tooth structure.

It is to be noted that the term fitting is not to be interpreted in thenarrow sense that the overlay should closely surround the teeth. Itmoreover should be interpreted as that an overlay should surround theteeth so as to be adequately in contact with the teeth and so that, onceapplied, it will not be released even if certain pressure, due to anormal use of the overlay, is applied.

Preferably, the method of this invention further comprises the steps of:

acquiring three-dimensional data relating to a shape of at least saidtooth and at least said part of said neighboring tooth;

processing said three-dimensional data with a computer so as todetermine significant dimensions and orientations for said overlay;

processing said three-dimensional data to determine said predeterminedpart.

Depending on the individual dental situation of a patient, the computeris programmed to determine an optimal way for shaping the tooth into ashape that is suitable for further treatment.

In a preferred embodiment of the invention, said first and said secondguiding edge are designed for simultaneously contacting said dentistcutting tool at contacting points being longitudinally distanced fromeach other by said distance, said guiding edges thereby defining aguiding surface along which said dentist cutting tool is to be guided.

By simultaneously contacting two guiding edges with a cutting tool atcontacting points being longitudinally distanced from each other, thecutting tool can be guided at least partially in a predetermined way.Preferably the cutting tool moves along the two guiding edges andthereby defines a guiding surface. This surface comprises the twoguiding edges, and a cutting tool can be guided along this surface. Thisallows an accurate guiding in two dimensions.

Preferably, said guiding means comprise a guiding groove, which definesa path extending in a surface of said overlay and suitable for guidingsaid dentist cutting tool along said path in such a manner as to enablea guided removal of at least partially said predetermined part of toothstructure.

The two guiding edges, being distanced from each other, can be locatedone on the one side and the other on the other side of the path therebydefining the path between the two guiding edges. To this purpose, thedistance between the two guiding edges should be substantially equal toa diameter of the cutting tool. Using the dentist cutting tool bysimultaneously contacting the two guiding edges and following the pathallows a guidance of the cutting tool at least in two dimensions.Considering a longitudinal cutting tool, the surface defined by the twoguiding edges in this configuration will be substantially perpendicularto the direction of the cutting tool in use. The preferred tilt of thecutting tool, in this configuration, is perpendicular to the plane thatis formed by the two guiding edges.

The two guiding edges, being distanced from each other, can also be bothlocated on one side of the path. At least a third guiding edge will thendefine the other side of the path. Considering a longitudinal cuttingtool in this configuration, the surface defined by the two guiding edgeswill be substantially parallel to the direction of the cutting tool inuse. The third guiding edge in this configuration will provide a furtherguidance to the cutting tool thereby increasing the accuracy of theprocess of removal of tooth structure. Using the dentist tool bysimultaneously contacting the two guiding edges and following the pathin this configuration allows a guidance of the cutting tool in twodimensions and a guidance of inclination of the cutting tool.

Preferably, the method comprises the further steps of:

producing a tooth restoration part having an inner shape determined soas to fit a predetermined remaining part of tooth structure of saidtooth, and having an outer shape determined so as to fit together withremaining neighboring teeth.

An advantage of the method according to the invention is that the shapeof the remaining part of tooth structure of the prepared tooth is knownin advance due to the guided removal of tooth structure. This improvesfurther treatment, such as preparing a temporary or final inlay, onlay,bridge, crown or veneer in advance based on the three-dimensional data.This results in that less office visits are required, as the dentist canboth prepare the tooth and mount the tooth restoration part onto theprepared tooth in one single visit. This way of working does not onlysave time and thus costs, also the inconvenience for the patient isstrongly decreased. Furthermore the chances that a prepared tooth getscontaminated, and the resulting complications, are reduced to a minimum.

Preferably, the method comprises the further steps of:

processing said three-dimensional data to simulate a tooth restorationpart having an inner shape determined so as to fit a predeterminedremaining part of tooth structure of said tooth, and having an outershape determined so as to fit together with remaining neighboring teeth;

producing said tooth restoration part.

Thereby, an individually designed tooth restoration part can bedelivered together with the dentist tool according to the invention.This is possible because the final shape of the prepared tooth, whenusing the dentist tool, is known in advance. The result is that lessdental visits are required to place a restoration part.

Preferably, said predetermined part is determined by:

firstly determining an outer shape of said tooth restoration part so isthat it fits together with remaining neighboring teeth, and determiningan inner shape of said tooth restoration part that is compatible withsaid outer shape;

secondly determining a shape of remaining tooth structure so that saidtooth restoration part having said inner shape fits said shape ofremaining tooth structure;

thirdly determining said predetermined part as being the part of toothstructure to be removed so as to have said shape of remaining toothstructure left.

Starting with determining a tooth restoration part instead of, asconventionally, preparing the tooth, has an advantage. A toothrestoration part can be determined having an outer shape so as tooptimally fit together with remaining neighboring teeth. Procedures fordetermination of such an outer shape are known to the person skilled inthe art. An inner shape is then determined, which inner shape iscompatible with said outer shape. Criteria for being compatible dependon the material that is to be used and mainly concern strengthparameters, production parameters and parameters relating to themounting of the restoration part onto the tooth and/or teeth. Preferablythe inner shape is determined in such a manner that a minimum amount ofmaterial is required to produce the tooth restoration part. This at itsturn results in that the remaining tooth structure, required to fit tothis inner shape, is as large as possible, namely, the more material ofa restored tooth is tooth restoration material, the less material ofthat restored tooth is tooth structure. Then the predetermined part canbe determined as being the part of tooth structure to be removed so asto have said shape of remaining tooth structure left. Thus firstdetermining the tooth restoration part, results in that a minimum oftooth structure is to be removed from the tooth and maximum conservationof the original tooth structure. As it is best to maintain as much ofthe original tooth structure, this is an advantage.

Providing the determined tooth restoration part having the determinedouter and inner shape together with the dental tool, results in thatless office visits are required because the dentist can prepare thetooth and mount the tooth restoration part onto the prepared tooth inone single visit.

Preferably said dentist tool comprises at least one further overlay,said overlay and said at least one further overlay being determined toguide a dentist tool in removing tooth structure in a plurality ofstages, in which said guiding means in said overlay is provided to guidesaid cutting tool in one of said plurality of stages, and at least onefurther guiding means in said at least one further overlay is providedto guide said cutting tool in at least one further of said plurality ofstages, the method further comprising the steps of:

determining at least one further overlay fitting said tooth and fittingat least a part of said neighboring tooth;

simulating at least one further movement to be followed by said dentistcutting tool in order to remove at least one further part of saidpredetermined part;

determining at least one further first guiding edge within said at leastone further overlay, said at least one further first guiding edgecorresponding to said at least one further movement so that it isprovided to contact said dentist cutting tool following said at leastone further movement, thereby being provided to guide said dentistcutting tool in a predetermined position, said at least one furtherfirst guiding edge being part of said at least one further guidingmeans;

determining at least one further second guiding edge within said atleast one further overlay that is spaced apart from said at least onefurther first guiding edge by a distance d of at least 0.5 mm, said atleast one further second guiding edge corresponding to said at least onefurther movement so that it is provided to simultaneously with said atleast one further first guiding edge contact said dentist cutting toolfollowing said at least one further movement, said at least one furtherfirst and second guiding edge thereby being provided to guide saiddentist cutting tool in a predetermined tilt, said at least one furthersecond guiding edge being part of said at least one further guidingmeans

producing said at least one further overlay with said at least onefurther guiding means.

Producing a plurality of overlays instead of just one overlay provides afurther flexibility in the method for producing the dentist tool.Different overlays can be provided for guiding a dentist cutting toolalong different sides of the tooth to be prepared, so that for example acircumferential path can be defined by using multiple overlays eachdefining a different segment of the circumferential path. Multipleoverlays furthermore allow to use different dental cutting tools, whichis necessary in some cases. Different overlays can be provided forpreparing a tooth in multiple stages, in which for example a first stageis provided to smoothen the upper part of the tooth, a second and athird stage are provided to cut away the longitudinal and transversalsides of the tooth, and a fourth and fifth stage are provided to roundoff the edges between the longitudinal and transversal sides each at adifferent side of the tooth. Preparing a tooth in stages allows eachoverlay to be designed having guiding edges which are particularlydetermined for guiding the cutting tool in a particular waycharacterized by the particular stage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more details with respect to thedrawings illustrating some preferred embodiments of the invention. Inthe drawings:

FIG. 1 shows a top view of an overlay with a guiding groove according tothe invention;

FIG. 2 shows a side view of an overlay with a guiding groove placed ontoa patient's teeth.

FIG. 3 shows a cross section of part of an overlay with guiding meansaccording to one embodiment of the invention and a cutting tool;

FIG. 4 shows a cross section of part of an overlay with guiding meansaccording to another embodiment of the invention and a cutting tool;

FIG. 5 shows a cross section of part of an overlay with guiding meansaccording to the invention and a cutting tool;

FIG. 6 shows a cross section of part of an overlay with guiding meansaccording to a further embodiment of the invention and a cutting tool;

FIGS. 7A-7E show various stages for the removal of tooth structure forpreparing a tooth for mounting a crown or a bridge.

FIG. 8 shows a cross-section of the overlay shown in FIG. 7A.

DETAILED DESCRIPTION

In the drawings a same reference number has been allocated to a same oranalogous element.

The terms “lower”, “upper” etc. and derived directional terms such as“horizontal” and “vertical” are based on a normal configuration of anoverlay as shown in the drawings, wherein the overlay fits onto teethwith their root extending vertically downward. The term dentist in thistext is not to be interpreted restrictive and can also be read as dentaltechnician, dental assistant, dental auxiliary, dental therapist, dentaldesigner etc.

The invention provides a method for producing a dentist tool formed byan overlay 1 to be used by a dentist in removing tooth structure.Furthermore, the invention provides an overlay 1 obtainable by thismethod. FIGS. 1 and 2 show such an overlay 1 arranged onto the teeth 2of a patient. Preferably, the invention provides a method for producingthe dentist tool and a tooth restoration part in such a manner that thetooth restoration part will fit the tooth that is prepared using thedentist tool.

The dentist tool according to the invention is preferably used by adentist in preparing a tooth for a restoration such as placing inlaysand onlays, crowns, bridges, and veneers. Such restoration requires arestoration part to be produced in order to fit the tooth after thelatter has been prepared. Using the dentist tool according to theinvention results in that the shape of the prepared tooth, whichconventionally is only known after preparation, is determined inadvance. Based on this knowledge, a restoration part can be produced inadvance so that this restoration part is available to the dentist evenbefore he or she starts preparing the tooth, and can be mounted directlyafter preparation of the tooth. This results in that the patient suffersless inconvenience, in particular that the number of visits to thedentist are reduced. Furthermore the chances that a prepared tooth getscontaminated, and the resulting complications, are reduced to a minimum.

Preferably, preparing a tooth for further treatment is performed onto asubstantially healthy tooth. When a tooth is damaged or infected, thedamaged and/or infected parts of the tooth will have to be removedfirst, and the tooth will have to be reconstructed before preparing thetooth for further treatment. This minimizes the chance that an infectiondevelops underneath a tooth restoration part. This also maximizes thelifetime of the tooth restoration part as the basis for the toothrestoration part, namely the tooth, does not contain damaged parts anymore.

It may be possible to utilize an overlay made for one tooth in thepreparation of a tooth of another patient, where such other patient'stooth has sufficiently similar dimensions and shape. Therefore, it iswithin the scope of this invention to have prepared some overlays whichcan be standardized, reused and/or reproduced. Also, it is within thescope of this invention to utilize data obtained in the preparation ofprior overlays and restoration parts in the design and generation of newoverlays having substantially similar dimensions and shapes.

Several methods are known for acquiring three-dimensional data from apatient's dentition. Such data can be retrieved, for example byprocessing photographs taken from the patient's dentition. Anothermethod is making a physical impression of the dentition and thensubsequently scanning this impression or a reversed cast of theimpression. Such scanning can be conducted with a CAD/CAM 3D scanningdevice. Illustrative of such a device is the FreeForm® from SensAbleTechnologies Inc. of Woburn, Mass., USA. While such a scanning devicecan scan a model of the dental arch with a tolerance of about 10 μm thisdoes not take into account other error factors obtained from the makingof the impression and the casting of the dental impression. In preparingthe ultimate restoration part or dental prosthesis, these other errorfactors or tolerances must be considered.

The CAD program chooses the specific configuration for the overlay,sometimes referred to as reduction trays, and ultimately theconfiguration for the prepared tooth by utilizing certain protocolswhich are based on prior experience for preparing dental prostheses.

In one embodiment of the invention, the digital file for the subjecttooth can be compared with an existing database for such prostheses.Such an illustrative database is available from Heraeus Kulzer ToothLibrary of Heraeus Kulzer GmbH of Hanau Germany. This data base has alsobeen integrated into the SensAble Dental Lab System (SDLS). A prosthesis(e.g. a crown or onlay) comparable to that appropriate for the subjecttooth is chosen from the Kulzer database. That prosthesis informationincludes the configuration and dimensions for the prepared tooth, whichwould correspond to the internal surface of the prosthesis. Thisinternal configuration in the Kulzer database for that prepared crown isutilized to design the overlays (reduction trays) for use in thepreparation of the patient's tooth. In the design of the overlays,fundamental principles and objectives known in the art are utilized, forexample to remove the minimum amount of original tooth surface.

For example, in a set of overlays or reduction trays, there may be oneoverlay or tray for reduction of the medial and distal surface (frontand back) and another tray for the occlusive (top) surface. Also, therecould be two finishing trays which cut lingual (tongue) surface andbuccal (cheek) surface of the tooth. For preparation for a crown, onewould need additional trays for gingival margins.

The foregoing describes a typical use of the method but a greater orfewer number of reduction trays or overlays may be appropriate to carryout the preparation of the tooth for later installation of the dentalprosthesis or restoration part. After acquiring the three-dimensionaldata of the tooth, this data gets processed by a computer so as todetermine an overlay 1 fitting the teeth 2 of the patient. To this end,the inner shape of the overlay preferably corresponds to the outer shapeof the tooth to be prepared and to the outer shape of at least part of aneighboring tooth. Overlay should fit the teeth in such a manner thatonce the overlay is placed onto the teeth, it will only come off byapplying a sufficiently high force to the overlay. During preparation ofthe tooth, small forces may be applied to the overlay, which preferablyshould not modify the position of the overlay on the teeth. Preferably,the overlay 1 extends over the teeth 2 so as to also cover part of thegingiva 3 or of neighboring teeth for stability purpose and protectionpurpose. As the dentist will use the overlay 1 for removing toothmaterial, it is advantageous that the overlay 1 is located onto thetooth in a stable way. As an example, an overlay 1 closely fitting thetooth, two neighboring teeth, and part of the gingiva 3, ensures that adentist can arrange and maintain the overlay in a stable position duringremoval of tooth structure. When the overlay 1 covers a part of thegingiva 3, at least this part of the gingiva 3 will be protected duringthe process of removing tooth structure.

It is to be noted that an overlay 1 according to the invention can covermultiple teeth at once and can be provided to be used by a dentist inpreparing a plurality of teeth using one single overlay 1. This can beadvantageous in the process of preparing teeth for placing veneers. Suchan overlay comprises guiding means, as will be explained further, foreach tooth that needs to be prepared.

The determined overlay 1 has a thickness 4 that mainly depends on therequired strength thereof, and thus also the material it will be madeof. An overlay 1 according to the invention can have a constant overallthickness 4. A substantially constant overall thickness is preferred foran overlay to be used by a dentist in preparing a tooth or teeth forplacing veneers. An overlay to be used for preparing a tooth for placinga bridge or a crown preferably comprises an upper, guiding part 5, and alower, supporting part 6. The supporting part 6 of the overlay 1 willensure that the overlay 1 can be arranged in a stable way onto the teeth2, whereas the guiding part 5 of the overlay 1 will guide the dentistcutting tool and preferably will also determine the maximal penetrationdepth of the cutting tool in the tooth. To this end, the thickness ofthe guiding part 5 of the overlay 1 will preferably be determined caseby case together with the determination of the guiding means 7, as willbe explained further. The thickness 4 of the supporting part 6 of theoverlay 1 can be more freely chosen depending on the preferences of thedentist and/or the programmation of the computer.

After acquiring the three-dimensional data, this data gets alsoprocessed by a computer so as to determine a predetermined part of toothstructure to be removed from the tooth by the dentist. The predeterminedpart will be determined in view of the further treatment. If aparticular shape of the prepared tooth is required for allowing furthertreatment, the predetermined part will be chosen so that afterpreparation of the tooth, this particular shape will remain.

Determining the predetermined part depends on many parameters and willdiffer from case to case. Parameters are the location of the tooth inthe mouth of the patient, amount and location of the damaged toothstructure, distance of the tooth to neighboring teeth, etc. In apreferred embodiment, the computer will also take into account thedifferent parts of the tooth such as the enamel, dentin, pulp, cementum,etc. in determining the predetermined part. It is also understood withinthe general aspects of the invention that the patient's tooth may haveto be built up through conventional techniques and materials prior tothe actual step of preparation of the tooth, utilizing the overlay.

According to the invention, the computer is programmed to determine thepredetermined part of tooth structure to be removed without assistanceof a dentist except for what concerns the input of the initial data ofthe tooth. However also according to the invention, the computer can beprogrammed to determine the predetermined part in cooperation with adentist, where, for example, the dentist decides on some parameters.This cooperation can be established by visualizing data relating to thetooth onto a computer display and allowing the dentist at least to enterone parameter relating to the preparation of the tooth. Preferably apreview of the tooth is visualized onto the computer display togetherwith a preview of a simulation of the prepared tooth, so as to allow adentist to see the impact of chosen parameters onto the prepared tooth.The latter feature provides a larger degree of freedom to the dentistand allows a less experienced dentist to consult a more experienceddentist about a case, based on the data in the computer. In this manner,the method for producing a dentist tool according to the inventionallows a less experienced dentist to decide on a further treatment andprepare a tooth for further treatment with a same quality as if he orshe was an experienced dentist.

In another embodiment, the computer is programmed to determine thepredetermined part of tooth structure to be removed in several phases.At the end of each phase, the computer proposes a simulated solution tothe dentist and requests for approval or correction of the proposedsolution.

Preferably the predetermined part will be determined in several steps.In a first step, the outer shape of the tooth restoring part is to bedetermined so that the tooth restoring part fits with the remainingteeth and fits into the dental arch of the patient. A bite lift or othercorrective amendment can be directly integrated into the design of theouter shape. Then, based on this determined outer shape, an inner shapegets determined that is compatible with the outer shape. In such amanner, a tooth restoration part can be determined having an optimalouter shape, and an optimal construction in the sense that it is strongenough and a minimum of material is needed. In a following step, theshape of remaining tooth structure is to be determined so that the innershape of the tooth restoring part fits the remaining tooth structureafter removal of tooth structure. In a final step, the predeterminedpart of tooth structure is determined as the part of tooth structure tobe removed to have the shape of remaining tooth structure left. This wayof working allows determining the outer shape of the tooth restoringpart using best fit programs. Conventionally, the dentist will notfollow the steps in the succession as mentioned above. The dentist willwork the other way around, as the dentist will need to know the shape ofthe prepared tooth to determine the inner shape of the restoration part,after which the dentist will determine an appropriate outer shape.Firstly determining the tooth restoration part, according to a preferredembodiment of the invention, results in that a minimum of toothstructure is to be removed from the tooth and a maximum conservation ofthe original tooth structure can be obtained.

Once the predetermined part has been determined, guiding means can bedetermined. The purpose of the guiding means is to guide a dentistcutting tool, i.e. a drill, along a simulated movement whereby thecutting tool removes at least a part of the predetermined part. To thisend, it will be understood that in some cases, the dimensions of thedentist cutting tool, such as the length, diameter, cross-sectionalform, etc. will be determining for which movement is to be made with thecutting tool to remove a certain part of tooth structure. It will alsobe understood that in many cases, it will not be sufficient to make onesingle movement for removing all the predetermined part. Via computercalculation and/or simulation, one or more movements can be simulatedfor removing the predetermined part of tooth structure. It is to beunderstood that a movement in this context does not only relates to atwo-dimensional position, but relates to the movement of the cuttingtool in all its aspects such as horizontal movement, vertical movementand tilt movement.

The guiding means according to the invention comprise at least twoguiding edges 11, 12 (FIGS. 3-6). Two of these guiding edges 11, 12 arespaced apart from each other with a distance d of at least 0.5 mm. Theguiding edges 11, 12 are provided to simultaneously contact the cuttingtool 10 thereby guiding the cutting tool 10 at least partially into apredetermined movement. It is to be understood in this context that asurface having a length and having a width which are at least 0.5 mm canbe considered as the said at least two guiding edges 11, 12. Namely, thetwo outer edges of the surface are provided to simultaneously contactthe cutting tool 10, and are spaced apart with a distance d of at least0.5 mm.

The guiding edges 11, 12 are determined in correspondence with thesimulated movement of the dentist cutting tool such that both guidingedges 11 and 12 are simultaneously in contact with the cutting toolfollowing the movement. Preferably, the guiding edges are simultaneouslyand constantly in contact with the cutting tool, preferably during thewhole of the movement. The contact between a guiding edge and thecutting tool, along the movement, is preferably a point of contact.

Preferably the two guiding edges 11, 12 are spaced apart from each otherwith a distance d of at least 1 mm, more preferably of at least 2 mm andmost preferably of at least 3 mm Increasing the distance d between thetwo edges 11, 12 will increase the guiding quality as it will be mucheasier for a dentist to control the cutting tool 10 onto larger guidingmeans.

The guiding edges 11, 12 are provided in such a manner as to besimultaneously contacted by the cutting tool at two contacting points.As illustrated in FIG. 3, preferably these contacting points 11, 12,considered on the cutting tool 10, are longitudinally spaced apart bythe distance d. When the cutting tool 10 is arranged substantiallyperpendicular to the guiding edges, the distance between the contactingpoints will be substantially the same as the distance d between theguiding edges. FIG. 3 illustrates a cutting tool 10 lying simultaneouslyagainst the two guiding edges 11, 12. The guiding edges 11, 12 in thisconfiguration define a surface along which the cutting tool 10 can beguided.

However the guiding edges 11, 12 can also simultaneously contact thecutting tool 10 at two contacting points being located each at one sideof the cutting tool 10, as illustrated in FIG. 4. In this configuration,the guiding edges 11, 12 define a guiding groove in which the cuttingtool 10 can be guided. The guiding groove 7 is preferably determined soas to define a path laying in the upper surface of the overlay 1. Thegroove 7 is provided for guiding a dentist cutting tool along this path,and to this end, the groove 7 extends through the overlay so as to forma communication between the inside of the overlay and the outerenvironment. When more than one path is to be followed for removing thepredetermined part, multiple guiding grooves 7 will have to bedetermined.

A combination of these two mentioned configurations is illustrated inFIG. 5. In this figure, a first and second guiding edge 11, 12, beingthe two guiding edges that are spaced apart, can be seen on the lefthand side, which edges define a guiding surface. A third guiding edge 13can be seen on the right hand side, which edge defines, together withthe first and second guiding edge 11, 12, a path. This configurationtherefore allows a cutting tool to be guided into both a horizontalmovement and a tilt.

As can be seen in FIG. 5, the cutting tool 10 preferably comprises acollar 14 mounted onto the cutting tool 10. Preferably at least one ofthe guiding edges 11, 12, 13 is provided to guide the collar 14 of thecutting tool 10 thereby guiding the cutting tool 10 into a predeterminedvertical position or height or depth. As can be seen in the FIG. 5, theguiding groove 7 defining a horizontal path, furthermore defines apredetermined height 8 for each horizontal location of the cutting tool,so as to guide the cutting tool 10 along a horizontal path and in apredetermined tilt, and also guiding the cutting tool in the verticalway.

FIG. 6 illustrates a variant on the embodiment shown in FIG. 3, andshows the guiding edges 11, 12, which are provided to simultaneouslycontact the cutting tool at two contacting points being longitudinallydistanced from each other. In this embodiment, tooth structure can beremoved that is located in between the two guiding edges 11, 12. Inparticular in preparing a tooth for placing veneers, this embodimentwill be used.

For mounting a crown or a bridge, the tooth is to be shaped into atruncated pyramid having rounded edges. To this end the outer and upperpart of the tooth are to be removed. This removal of tooth structure canbe guided by the dentist tool according to the invention.

Preferably the removal of tooth structure for preparing a tooth formounting a crown or a bridge is performed in several stages shown inFIGS. 7A-7E. In a first stage, shown in FIG. 7A and FIG. 8, the upperpart of the tooth gets smoothened. This can be done using an overlayhaving guiding edges 11, 12 as illustrated in FIG. 6. However inpractice, it is preferred that the upper part gets shaped into a V-form.To this end, the upper part preferably gets smoothened using two guidingmeans as illustrated in FIG. 3, which guiding means are located on bothsides of the tooth in such a manner that said guiding means are providedguide said cutting tool to cut said upper part into a V-shape.

In a second and a third stage, shown in FIGS. 7b and 7c , thelongitudinal and transversal sides of the tooth get cut, so as to obtaina truncated pyramid form. The cutting of these sides can be guided byoverlays having guiding means as illustrated in FIG. 3, 4 or preferablyFIG. 5. Preferably one overlay comprises two such guiding means eachdefining a path extending in the surface of the overlay, the pathsextending parallel to each other, each on one side of the tooth.

In a fourth and fifth stage, shown in FIGS. 7d and 7e , the edges of thepyramid get rounded. Rounding these edges can be guided by an overlay asshown in FIGS. 1 and 2. Such an overlay comprises a path extending inthe surface of the overlay and defining a segment of a circle. Each sideof the path is defined by a guiding surface having at least two guidingedges, as illustrated in FIG. 3. The height of the guiding part 5 of theoverlay 1 is defined so as to guide the cutting tool 10 in apredetermined vertical position.

In this succession of stages, the first stage could be executed as thelast stage instead of as the first. However tests have shown thatstarting with smoothening the upper part of the tooth is advantageous inthe process of preparing the tooth.

Once the overlay 1 and the guiding means are determined, the determinedoverlay 1 having the determined guiding means can be produced. This canbe done by any known means such as a CAD/CAM system, rapid prototypingor 3D printing. When multiple guiding means have been determined,multiple overlays 1 can be produced each comprising one or severalguiding means. Preferably, a rapid prototyping apparatus creates theoverlay with a tolerance of about 30 μm.

The overlay 1 has, as already mentioned above, a lower, supporting part6 and an upper, guiding part 5. As can be seen in the figures, theguiding part 5 has a certain thickness 8, which defines the height 8 ofthe path and enables the cutting tool to be guided in the vertical way.Preferably the supporting part 6 and/or guiding part 5 comprises avertical opening 9 from the side to the guiding groove 7, provided toserve as an entrance into the guiding groove 7 for a dental cuttingtool. In particular when a cutting tool has a tip portion that has adiameter that is larger than the diameter of the main portion of thecutting tool, for example a high-speed drill with a tip in the form of aball, this opening is advantageous. Entering such a cutting tool intothe guiding groove 7 via the upper part of the overlay would at leastpartially widen the guiding groove 7 thereby at least partially takingaway its possibility to firmly guide the cutting tool along thepredetermined path. Furthermore a side entrance 9 is preferred over anentrance via the upper part as it will be easier to enter the cuttingtool in a controlled manner into the guiding groove 7.

When a guiding groove 7 is determined to form a circular path in thehorizontal plane, it will be preferred to split up this path intoseveral segments, and produce multiple overlays 1 each having a guidinggroove 7 corresponding to one segment of this path. This will result ina set of overlays 1 which can be used by a dentist one after the otherto remove tooth structure following this circular path. Each overlay 1of the set of overlays 1 will guide the cutting tool along a particularside of the tooth.

In the embodiment where the predetermined part is not determined basedon the shape of the tooth restoration part, the latter can be determinedbased on the data in the computer. Outer shape of the tooth restorationpart can be determined in several ways, all known to the person skilledin the art. A bite lift or other corrective amendment can be directlyintegrated into the design of the outer shape. A first possibility is toshape the tooth restoration part so that it resembles the outer shape ofthe original tooth. A second possibility is to shape the toothrestoration part so that it fits with neighboring teeth. A thirdpossibility is a combination of the first and second, and modifies theshape of the original tooth to better fit with the neighboring teeth.Inner shape of the tooth restoration part will be determined based onthe simulation of the preparation of the tooth. As the tooth will beprepared in a guided manner, it is known in advance what the shape willbe of the prepared tooth. The inner shape of the tooth restoration partwill be chosen so that it fits the shape of the prepared tooth.

Preferably the method according to the invention further comprises thestep of producing a tooth restoration part.

Similar to the determination of the predetermined part, a toothrestoration part can be determined by a computer without any interactionof a dentist. However it will be preferred that the computer determinesthe tooth restoration part in cooperation with a dentist, for example ina way as described above. The computer can, in this process ofdetermining a tooth restoration part, perform predetermined clinicalchecks and alert the dentist in case the tooth restoration part does notmeet the standard norms. This will enable a dentist to design a toothrestoration part in a fast and reliable manner.

The production of the tooth restoration part can be done by any meansknown to the skilled person such as a CAD/CAM system.

1. Method for producing a dentist tool formed by an overlay (1) to beused by a dentist in removing tooth structure from a tooth, said methodcomprising the steps of: determining a predetermined part of toothstructure to be removed so as to prepare said tooth for furthertreatment; determining an overlay (1) fitting said tooth and fitting atleast a part of a neighboring tooth of said tooth; simulating a movementto be followed by a dentist cutting tool in order to remove at least apart of said predetermined part; determining a first guiding edge (7)within said overlay (1), said first guiding edge corresponding to saidmovement so that it is provided to contact said dentist cutting toolfollowing said movement, thereby being provided to guide said dentistcutting tool in a predetermined position, said first guiding edge beingpart of a guiding means; producing said determined overlay with saidguiding means, characterized in that said method comprises the furthersteps of: determining a second guiding edge within said overlay that isspaced apart from said first guiding edge by a distance d of at least0.5 mm, said second guiding edge corresponding to said movement so thatit is provided to simultaneously with said first guiding edge contactsaid dentist cutting tool following said movement, said first and secondguiding edge thereby being provided to guide said dentist cutting toolin a predetermined tilt, said second guiding edge being part of saidguiding means.
 2. Method according to claim 1, wherein the methodfurther comprises the steps of: acquiring three-dimensional datarelating to a shape of at least said tooth and at least said part ofsaid neighbouring tooth; processing said three-dimensional data with acomputer so as to determine said overlay (1); processing saidthree-dimensional data to determine said predetermined part.
 3. Methodaccording to claim 1, characterised in that said first and said secondguiding edge are determined for simultaneously contacting said dentistcutting tool at contacting points being longitudinally distanced fromeach other by said distance d, said guiding edges thereby defining aguiding surface along which said dentist cutting tool is to be guided.4. Method according to claim 1, characterised in that said guiding meanscomprise a guiding groove, which defines a path extending in a surfaceof said overlay and suitable for guiding said dentist cutting tool alongsaid path in such a manner as to enable a guided removal of at leastpartially said predetermined part of tooth structure.
 5. Methodaccording to claim 1, characterised in that the method comprises thefurther steps of: producing a tooth restoration part having an innershape determined so as to fit a predetermined remaining part of toothstructure of said tooth, and having an outer shape determined so as tofit together with remaining neighbouring teeth.
 6. Method according toclaim 2, characterised in that the method comprises the further stepsof: processing said three-dimensional data to simulate a toothrestoration part having an inner shape determined so as to fit apredetermined remaining part of tooth structure of said tooth, andhaving an outer shape determined so as to fit together with remainingneighbouring teeth; producing said tooth restoration part.
 7. Methodaccording to claim 6, characterised in that said predetermined part andsaid tooth restoration part is determined by: firstly determining anouter shape of said tooth restoration part so that it fits together withremaining neighbouring teeth, and determining an inner shape of saidtooth restoration part that is compatible with said outer shape;secondly determining a shape of remaining tooth structure so that saidtooth restoration part having said inner shape fits said shape ofremaining tooth structure; thirdly determining said predetermined partas being the part of tooth structure to be removed so as to have saidshape of remaining tooth structure left.
 8. Method according to claim 1,characterised in that said dental cutting tool comprises a cuttingportion and a collar, one of said first and second guiding edges beingdesigned to guide said collar along so as to enable said dentist cuttingtool to be guided into a predetermined depth.
 9. Method according toclaim 1, characterised in that said dentist tool comprises at least onefurther overlay, said overlay and said at least one further overlaybeing determined to guide a dentist tool in removing tooth structure ina plurality of stages, in which said guiding means in said overlay isprovided to guide said cutting tool in one of said plurality of stages,and at least one further guiding means in said at least one furtheroverlay is provided to guide said cutting tool in at least one furtherof said plurality of stages, the method further comprising the steps of:determining at least one further overlay fitting said tooth and fittingat least a part of said neighbouring tooth; simulating at least onefurther movement to be followed by said dentist cutting tool in order toremove at least one further part of said predetermined part; determiningat least one further first guiding edge (7) within said at least onefurther overlay (1), said at least one further first guiding edgecorresponding to said at least one further movement so that it isprovided to contact said dentist cutting tool following said at leastone further movement, thereby being provided to guide said dentistcutting tool in a predetermined position, said at least one furtherfirst guiding edge being part of said at least one further guidingmeans; determining at least one further second guiding edge within saidat least one further overlay that is spaced apart from said at least onefurther first guiding edge by a distance d of at least 0.5 mm, said atleast one further second guiding edge corresponding to said at least onefurther movement so that it is provided to simultaneously with said atleast one further first guiding edge contact said dentist cutting toolfollowing said at least one further movement, said at least one furtherfirst and second guiding edge thereby being provided to guide saiddentist cutting tool in a predetermined tilt, said at least one furthersecond guiding edge being part of said at least one further guidingmeans producing said at least one further overlay with said at least onefurther guiding means.
 10. Method according to claim 9, characterised inthat said overlay and said at least one further overlay form a set ofoverlays to be used by a dentist in removing tooth structure for placinga crown or a bridge or an onlay, said set of overlays comprise fiveoverlays in which: a first overlay is determined for guiding a dentistcutting tool to smoothen an upper part of the tooth thereby consideringthe desired height of the remaining tooth structure; a second overlay isdetermined for guiding a dentist cutting tool to cut away one of thelongitudinal or transversal sides of the tooth; a third overlay isdetermined for guiding a dentist cutting tool to cut away the other ofthe longitudinal or transversal sides of the tooth; a fourth overlay isdetermined for guiding a dentist cutting tool to round off edges betweenthe longitudinal and transversal sides of the tooth at one side of thetooth; a fifth overlay is determined for guiding a dentist cutting toolto round off edges between the longitudinal and transversal sides of thetooth at the other side of the tooth.
 11. Method according to claim 1,characterised in said overlays are produced via rapid prototyping. 12.Method according to claim 1, characterised in that said distance d is atleast 1 mm, preferably at least 2 mm, more preferably at least 3 mm,most preferably at least 4 mm.
 13. Dentist tool (1) to be used by adentist in removing tooth structure from a tooth of a patient, whichtooth is to be prepared for further treatment, said dentist tool (1)comprising: an overlay having a shape and dimensions so that it isreleasably fixable to said tooth and to at least a part of aneighbouring tooth of said tooth; a first guiding edge within saidoverlay that is provided to contact a dentist cutting tool following apredetermined movement, said first guiding edge thereby being providedto guide said dentist cutting in a predetermined position, characterisedin that the dentist tool further comprises: a second guiding edge withinsaid overlay, said second guiding edge being spaced apart from saidfirst guiding edge by a distance d of at least 0.5 mm, said secondguiding edge being provided to simultaneously with said first guidingedge contact said dentist cutting tool following said predeterminedmovement, said first and second guiding edges thereby being provided toguide said dentist cutting tool in a predetermined tilt.
 14. Set ofoverlays (1) to be used by a dentist in removing tooth structure from atooth of a patient, which tooth is to be prepared for further treatment,said set of overlays (1) being obtained by the method as claimed inclaim
 9. 15. Method for preparing a tooth for further treatment using anoverlay according to claim 13.